Breast cancer is one of the leading causes of death for women. About one out of eight or nine women are expected to develop tumors of the breast, and about one out of sixteen to twenty are expected to die prematurely from breast cancer.
Mammography or other X-ray methods are currently most used for detection of breast cancers. However, every time a mammogram is taken, the patient incurs a small risk of having a breast tumor induced by the ionizing radiation properties of the X-rays used during the mammogram. Also, the process is costly and sometimes imprecise. Accordingly, the National Cancer Institute has not recommended mammograms for women under fifty years of age, who are not as likely to develop breast cancers as are older women. However, while only about twenty percent of breast cancers occur in women under fifty, data suggests that breast cancer is more aggressive in pre-menopausal women. Furthermore, women under forty are getting the disease in increasing numbers—about eleven thousand annually now—and no one knows why.
Mammograms require interpretation by radiologists. Radiologist can identify cancers between five and ten millimeters in diameter. Generally, when detected at this stage, the prognosis is favorable. However, about ten to fifteen percent of tumors this size are not detected. One study showed major clinical disagreements for about one-third of the same mammograms that were interpreted by a group of radiologists. Further, many women find that undergoing a mammogram is a decidedly painful experience.
Thus, alternative methods to detect breast cancer are needed, especially those that do not entail added risks; that can detect tumors as small as two millimeters in diameter; that are not unduly unpleasant to the patient; and that can be used for mass screening. A screening system is needed because extensive studies have demonstrated that early detection of small breast tumors leads to the most effective treatment. While X-ray mammography can detect lesions of approximately five mm or larger, the accuracy may range between 30% and 75%, depending on the skill of the diagnostic radiologist. Repeated X-ray examinations, however, are not encouraged because, as discussed above, may actually induce cancer formation. These considerations, in addition to costs, have led physicians to recommend that women wait until the age of fifty before having routine mammograms.
One solution would be a non-ionizing, noninvasive, and low cost detection or screening method. It could greatly increase the number of patients examined and would identify those patients who need diagnostic X-ray examinations, where the added hazards and costs could be justified. Thus, there is a need for a low-cost, noninvasive, screening method.
There are several generic detection methods: sonic, chemical, nuclear and non-ionizing electromagnetic. The sonic, chemical and nuclear (such as MRI) techniques have been under study for some time and, while some interesting approaches are being followed, none have been publicized as being available in the near future for low cost screening.
Non-ionizing electromagnetic methods have also been under investigation. Studies have considered the use of electromagnetic, non-ionizing methods to detect or image portions of the human body. One summary of such activity is presented in a publication entitled “Medical Applications of Microwave Imaging.” edited by L. E. Larsen and J. H. Jacobi, IEEE Press 1986. These activities include microwave thermography, radar techniques to image biological tissues, microwave holography and tomography, video pulse radar, frequency modulation pulse compression techniques for biological imaging, microwave imaging with diffraction tomography, inverse scattering approaches, and medical imaging using an electrical impedance. The technology cited not only includes electromagnetic disciplines, but also notes related studies in sonic imaging and seismic imaging.
Many important reasons exist for the lack of progress in these areas. In the case of microwave thermography, adequate depth of penetration, along with the required resolution, may not be realized, except for large cancers. In the case of other techniques using electromagnetic activities, reflections at the skin-air surface tend to mask the desired returns from breast tumors beneath the skin. Further, illuminating the entire volume of a breast either requires excessive power (with possible biological hazards) or acceptance of poor signal-to-noise rations. In the case of through-the-body electromagnetic techniques, such as tomography, the attenuation characteristics of the body are such that long wavelengths are usually used, with an attendant loss of resolution. Another important reason for the lack of progress is the degradation of sensitivity due to insufficient characterization techniques available for the antenna setups in near field. As the usable wavelengths are restricted by the attenuation characteristics of the body, all known techniques have to place the sensors, like antennas or antenna arrays, in close vicinity of the body parts to be examined.
Far field systems have been developed to overcome these limitations by placing the antennas at a distance of at least five to ten wavelengths away from the surface of the body part under examination so the signal being radiated has local plane-wave characteristics in order to correctly interpret the reflected measured response. Further, increasing the distance helps to minimize changes of the antenna characteristics through distortions of the electromagnetic field caused by direct interactions between the antenna structures and the body parts under examination. Additionally, multiple reflections between the antennas of the system and the skin-air interface of the body parts under examination may mask the desired returns from tumors and degrade the capability to detect cancers. Far field systems also require the use of much higher frequencies than near field system to reduce the absolute distance between antenna and the surface of the body parts to be scanned, as the far field regions is defined as a distance of at least ten wavelengths.
Certain near field systems have been described in the literature immersing the antenna/antennae and body parts under examination into a homogenous liquid solution with dielectric properties similar to the body parts in an attempt to make accurate measurements. While this approach helps to reduce some of the effects to a certain amount, it adds inconveniencies to the examination. The additional measures to be taken to make components watertight adds significant costs to the system it-self. Even when using liquid solutions to reduce the reflections on the skin-air interface, the large variation in electrical properties between the breast tissues of different women at different ages account for mismatch errors during measurements, if the dielectric properties of the liquids don't exactly match those of the tissue.